Muscle loss on a GLP-1 and how to keep the muscle you have
Published September 2, 2026
If you have spent any time in GLP-1 forums, you’ve witnessed the concern: that the weight coming off is muscle rather than fat. It is a valid concern and the honest answer is more nuanced than the headlines. Some muscle does come off. How much of it depends largely on what you do while you are losing weight.
What the data shows
Substantial weight loss by any method, includes some muscle loss along with fat. The key question is to examine the ratio of fat to muscle lost. In a body-composition study of the STEP 1 trial, adults on semaglutide for 68 weeks lost 19.3% of their fat mass and 9.7% of their lean body mass. On average, body composition improved because fat weight decreased more than muscle and the proportion of lean mass in the body rose. (Lean mass includes muscle as well as other non-fat body components, such as skin, water, connective tissue, bone and vital organs).
Across recent trials, lean mass loss averages between 25% to 39% of the total weight lost with GLP-1 therapy alone. With added exercise and resistance training in GLP-1 users, lean and bone mass is preserved.
Why muscle matters
Muscle does more than power your strength. It is metabolically active tissue, so it burns more energy at rest than fat does. This helps protect the metabolism you are working to improve. Muscle carries strength, balance and function — the things that shape how well you move and age. It also supports bone function. Because we lose muscle naturally with age (particularly in menopause), anyone in midlife has a greater reason to guard it.
How to keep the muscle you have
The muscle you keep can be in your control and the levers are well-established.
Eat enough protein. Protein gives your body the raw material to build or maintain muscle during weight loss. The right target is individual, often in the range of 1.0 to 1.6 grams per kilogram of body weight per day, depending on BMI and age. It does take some planning to consume adequate protein when the medication has lowered your appetite. Its best to work with a clinician to determine your specific protein intake target and strategies to meet this goal.
Do resistance training. Lifting, bands or bodyweight work a few times a week is the strongest signal you can send your body to keep muscle while fat comes off. In a case series of patients who trained several days a week and consumed adequate amounts of protein, some preserved and even gained lean tissue while losing weight on these medications.
Lose weight at a sensible pace. Slower weight loss serves you better here. A steady rate of loss (1 to 2 pounds per week) gives your body a better chance of maintaining muscle than rapid weight loss.
Measure more than the scale. A regular scale cannot tell muscle apart from fat. Body composition shows over time the type of body tissue you are losing and it allows you to adjust the plan before too much muscle goes with it.
Why a plan beats a prescription
This is the gap between a physician-led plan and a mailed prescription plan. A prescription-only service may send the medication and leave the comprehensive planning to you. A physician can set your protein target, guide your training, watch your body composition over time and adjust the plan so the weight you lose minimizes muscle loss.
The bottom line
Some muscle loss is expected with a GLP-1 or with any other strategy for weight loss. Muscle is protective and necessary for metabolic health, balance and longevity. How much muscle is lost can be modified with careful planning. By consuming adequate protein, implementing regular resistance training, losing weight at a reasonable pace and paying attention to body composition, fat loss can be prioritized over muscle.